Power control in orthogonal sub-channels in wireless communications

ABSTRACT

A method and apparatus for power control in a wireless communication involves establishing at least two orthogonal sub-channels within a channel for communication and controlling transmitted power in each sub-channel independently.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/914,879 filed Jun. 11, 2013, which is a continuation of U.S. patentapplication Ser. No. 12/058,495 filed Mar. 28, 2008, which issued asU.S. Pat. No. 8,467,408 on Jun. 18, 2013, which claims the benefit ofU.S. Provisional Application Ser. No. 60/909,006 filed Mar. 30, 2007,the contents of which are hereby incorporated by reference herein.

FIELD OF INVENTION

The present application is related to wireless communications.

BACKGROUND

The concept of Orthogonal Sub-channels (OSCs) and how they can be usedto increase the voice capacity of GSM EDGE Radio Access Network (GERAN)cells has been disclosed by others (GSM is Global System for Mobile;EDGE is Enhanced Data rates for Global Evolution). In an OSC scheme, thebase station (BS) uses Quadrature Phase-Shift Keying (QPSK) modulationfor downlink (DL), which multiplexes voice data from two users. Themultiplexing is done such that legacy Mobile Stations (MSs) usingGaussian Minimum Shift Keying (GMSK) can receive their respective data.

As an example, FIG. 1 shows a QPSK constellation chosen as a subset ofan Eight Phase Shift Keying (8PSK) constellation. The most significantbit (MSB) and least significant bit (LSB) define two “orthogonal”sub-channels I and Q, wherein the bits are denoted as (OSC0, OSC1). Eachsub-channel carries voice signals of two users in the DL direction.GMSK-only capable MSs are able to detect the individual sub-channels.

These prior OSC proposals also provide that downlink power control mayuse conditions of the weakest link as criteria. For example, in such anapproach, if the weaker orthogonal sub-channel is I, the power controlwould be adjusted such that both sub-channels I and Q are equallyincreased until the sub-channel I attains the minimum acceptable powerlevel. This approach would have the advantage of maintaining the shapeof the QPSK constellation as circular, keeping all four constellationpoints equidistant, which provides maximum separation for best receiverdecoding results. The disadvantage to this approach is that more poweris used than is necessary on the sub-channel that is not the weakestlink, (i.e., sub-channel Q in this example). Consequently, theinterference between the sub-channels will increase.

SUMMARY

A method and apparatus for multi-user communication includes independentpower control to each sub-channel designated to a user. A modified QPSKmodulation mapping is performed for two users, each user being assignedto an orthogonal sub-channel. The power control method minimizestransmitted power on each sub-channel and interference between eachsub-channel.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following descriptionof a preferred embodiment, given by way of example and to be understoodin conjunction with the accompanying drawing, wherein:

FIG. 1 shows a QPSK constellation chosen as a subset of an Eight PhaseShift Keying (8PSK) constellation and defining orthogonal sub-channels;

FIG. 2 shows a block diagram of a wireless communication with orthogonalsub-channel power control of a downlink signal; and

FIGS. 3A and 3B show orthogonal sub-channel I and Q constellations for amodified QPSK modulation with independent power control.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 2 shows a base station 201, comprising a processor 202 configuredto perform a method of a first embodiment. The processor 202 processesdata from users 251, 252 via the communication network 231, to betransmitted to a WTRU 211 and a WTRU 221 on a wireless downlink signal215. In order to increase capacity on the downlink signal 215, a radioresource can be mapped by the processor 202 whereby voice or datasignals from two users 251, 252 sent in the same time slot can beindividually detected by the intended receivers WTRUs 211 and 221. Amodified QPSK modulation is applied to the downlink signal 215 usingorthogonal sub-channels I and Q.

FIGS. 3A and 3B show examples of constellations for mapping of theorthogonal sub-channels I and Q according to a modified QPSK modulation,where power control is adjusted independently on each sub-channel I andQ. In FIG. 3A, a constellation 301 is rectangular along the Q axis, as aresult of independent power adjustment upward on the sub-channel I,while applying zero power adjustment to sub-channel Q. Alternatively,there may also be some independent power control adjustment on theQ-sub-channel, so long as the relative increase in power controladjustment on the sub-channel I is greater than that on thesub-channel-Q.

Conversely in FIG. 3B, a constellation 302 is rectangular along the Iaxis, which results when independent power control adjustment isincreased more on the sub-channel Q than on the sub-channel I.

Alternatively, there may be a decrease in power control adjustment toeither of the sub-channels I and Q.

Adaptive power control is independently applied on the sub-channels Iand Q, such that the rectangular constellation of the modified QPSKmodulation can vary according to an independent power control parameterα on the sub-channel I and an independent power control parameter β onthe sub-channel Q. For example, the four constellation points for themodified QPSK according to this embodiment can be represented as shownin Table 1:

TABLE 1 (0, 0) (0, 1) (1, 0) (1, 1) α + jβ α − jβ −α + jβ −α − jβ

The power control parameters α and β are constants set within thefollowing limits:

0<α≦1;

0<β≦1

where α and β are kept from approaching too close to 0. These parametersα and β represent the relative voltage amplitude for each of the twoorthogonal sub-channel I and Q signals, where α is proportional to thesquare root of sub-channel I power P_(I) and β is proportional to thesquare root of sub-channel Q power P_(Q). If the total power transmittedfor the two sub-channels I and Q is equal to P, then the power P_(I) ofthe sub-channel I is as follows:

P_(I)=α²P,

and the power P_(Q) of the sub-channel Q channel is:

P_(Q)≦β²P.

Practical implementation issues may constrain the ratio of α/β to bewithin limits. For example, one range for the ratio may be:

${0.5 < \frac{\alpha}{\beta} < 2},$

which would represent a practical constraint that the relative powerbetween the two sub-channels I and Q should not be greater than 4, orequivalently, 6 dB. The exact constraint will be a determined bypractical implementation issues, including, but not limited toquantization resolution of the analog to digital process.

Thus, the example constellations shown in FIGS. 3A and 3B each depictone of many possible variations, depending on the power controlparameter selected. The processor 202 determines the power controlparameters α and β depending on detected received channel qualityaccording to typical power control feedback schemes. One exampleincludes the processor 212 of WTRU 211 determining that the multipleerrors have been detected on received signal 215, and in response, achannel quality indicator (CQI) is reported back to the base station201. Based on the CQI, the processor 202 of base station 201 will selecta power control parameter α that will independently increase power onthe sub-channel I, which was allocated for the WTRU 211.

Various power control techniques can be applied to the orthogonalsub-channels I and Q, including open-loop based or close-loop basedschemes. Also, the time scale of the power control adaptation may beoptimally chosen. The criteria for power control adaptation may includesignal power, noise, or interference levels in any combination.

The criteria for power control adaptation also takes into accountdynamic range issues. For example, measures are taken to ensure that thetwo sub-channels I and Q are sufficiently close in power level toprevent the well-known signal capture problems that can occur when areceiver, such as the WTRU 211, must process two signals arriving atsignificantly different power levels. In particular, the captureproblems can occur at the WTRU 211 receiver during A/D conversion, wherean A/D converter dynamic range can be impacted by a large power leveloffset between received sub-channels I and Q. Maintaining a properbalance of the power levels can be achieved by the following twotechniques, either alone or in a combination thereof: (1) during ascheduling and channel assignment process, avoid assigning the twosub-channels I and Q to the WTRUs 211 and 221 with excessive differencesin required transmit power level; and (2) set the individual targetpower levels to values that support a proper balance. Optionally, anadditional, larger dynamic range can be achieved by specifying anincreased dynamic range capability for the mobile terminals (i.e. morebits in the A/D converter).

As part of the OSC modulation applied by the base station 201, a linkadaptation is performed for multiplexing the receivers WTRU 211 and WTRU221, by which the base station 201, or a Base Station System (BSS) towhich it belongs, can dynamically change the multiplexing based oncurrent channel conditions. Take for example, a scenario in which theWTRU 211 is located very close to the base station 201, and the WTRU 221is located relatively further away from the base station 201, and thesub-channels are multiplexed to the same time slot. Using internalthresholds and hysteresis, the base station 201 may elect to reassignthe WTRU 221 information from the multiplexed time slot and insteadmultiplex the WTRU 211 information with information of another WTRU thatis located closer to the base station 201. This can be achieved bysimple Intra-Cell Handover procedures, taking advantage of proceduressuch as “Packing/Unpacking”. As an alternative option, the base station201 may elect to have the WTRU 221 as the sole user of another timeslot.

The modified QPSK modulation method described above relates to thepacket-switched (PS) domain as follows. In PS domain, data is exchangedon channels, such as a Packet Data Channel (PDCH). An example of a PDCHis a time slot in a single carrier. The timeslot carries a radio burst,which is made up of a number of modulated symbols, each of which carriesone or more bits of data. All of these bits belong to the PDCH. In thepresent context, the bits associated with each symbol in the downlinkare assigned to multiple users, such as the WTRU 211 and the WTRU 221.For example, the MSB and LSB of the modified QPSK (i.e., (MSB, LSB)) maybe assigned as follows: MSB to the WTRU 211, LSB to the WTRU 221.Correspondingly, in the uplink, the WTRU 211 and the WTRU 212 transmiton the same time slot and the same carrier frequency, but usingdifferent (preferably orthogonal) training sequences. In thisembodiment, the definition of the PDCH is extended to such orthogonalsub-channels, referred to herein as Orthogonal-PDCH (O-PDCH). In theabove example, two O-PDCHs are defined in terms of the two orthogonalsub-channels in both the downlink and the uplink.

As an implementation of this embodiment, the WTRU 211 or the WTRU 221may receive a Packet Timing Control Channel (PTCCH) using an orthogonalsub-channel I or Q in the downlink. One advantage to this is that therewould be no need for the base station 201 to allocate a separate channelfor the PTCCH, and delay transmission of PTCCH information until anopportunity is available for the PTCCH transmission. Instead, the PTCCHinformation can be conveyed immediately on the I and Q sub-channels andreceived by the WTRU 211, 221 without delay. For uplink transmissions bythe WTRU 211 and 221, a normal PDCH may be used, (e.g., for case whereWTRUs 211, 221 are legacy devices). Alternatively, an O-PDCH may bedefined for the uplink, by which each of the sub-channels I and Q couldcarry a different data stream, or one sub-channel could carry datainformation and the other could carry voice or control information.

In an O-PDCH made up of more than one time slot, one or more time slotsmay carry orthogonal sub-channels I and Q, whereas other time slotssupport normal PDCH channels.

In order to uniquely identify the multiplexed WTRU 211 from the WTRU 221in the downlink 215, the base station 201 can send two different blocksof information, using the sub-channels I and Q, respectively to the WTRU211 and the WTRU 221. Within the same time slot, each block ofinformation contains a Temporary Flow Identity (TFI) in the header thatcorresponds to the sub-channel I or Q.

Within an uplink 225 signal, the WTRU 211 can be uniquely identifiedfrom the WTRU 221 by scheduling of resources based on an uplink stateflag (USF) parameter and/or the TFI. The scheduling of resources can beperformed by the base station 201 using the orthogonal sub-channels Iand Q to send two different USF values, one on each sub-channel, to theWTRU 211 and WTRU 221. When the WTRU 211 and WTRU 221 send informationin the uplink, they are uniquely identified by a unique mapping of theircorresponding TFI and the sub-channel number (e.g., 0 or 1). The basestation processor 202 detects the unique TFI and sub-channel number onthe received uplink, enabling unique identification of the WTRU 211 andWTRU 221 signals.

Finally, link adaptation can be applied to each O-PDCH by changingadaptively among various modulation and coding scheme (MCS) classes.Automatic Repeat Request (ARQ) with and without incremental redundancycan be applied for reliable transmission of data.

While embodiments have been described in terms of QPSK modulation, otherpossible variations may apply higher order modulations including, butnot limited to 8PSK, 16QAM and 32QAM, whereby the constellations mayreflect independent power control of sub-channels according to powercontrol parameter selection and adjustment.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A method for use in a first wirelesstransmit/receive unit (WTRU), for detecting transmissions for one of aplurality of users on a same physical resource, the method comprising:receiving, by the first WTRU, on a physical resource in a same timeslot, a first data for the first WTRU via a first one of in-phase andquadrature phase sub-channels on the physical resource and a second datafor a second WTRU via a second one of in-phase and quadrature phasesub-channels on the same physical resource, wherein a transmit power ofthe in-phase sub-channel and a transmit power of the quadrature phasesub-channel are independent of each other; processing, by the firstWTRU, the first data; and not processing, by the first WTRU, the seconddata.
 2. The method of claim 1 wherein a ratio of the transmit powerbetween the in-phase and quadrature phase sub-channels is within apredetermined range.
 3. The method of claim 1, wherein the transmitpower on the in-phase and quadrature phase sub-channels is based on atleast one of a signal power level, a noise level, and an interferencelevel on each sub-channel.
 4. The method of claim 1 wherein a targetpower value is set for the in-phase and quadrature phase sub-channels,respectively, to support a power balance between the in-phase andquadrature phase sub-channels.
 5. The method of claim 1 wherein thephysical resource is a time division multiple access (TDMA) resource. 6.A first wireless transmit/receive unit (WTRU) for detectingtransmissions for one of a plurality of users on a same physicalresource, comprising: a transceiver operatively coupled to a processor,the transceiver configured to receive on a physical resource in a sametime slot, a first data for the first WTRU via a first one of in-phaseand quadrature sub-channels on the physical resource and a second datafor a second WTRU via a second one of in-phase and quadraturesub-channels on the same physical resource, wherein a transmit power ofthe in-phase sub-channel and a transmit power of the quadraturesub-channel are independent of each other; the processor configured toprocess the first data; and the processor configured to not process thesecond data.
 7. The WTRU of claim 6 wherein a ratio of the transmitpower between the in-phase and quadrature phase sub-channels is within apredetermined range.
 8. The WTRU of claim 6 wherein the transmit poweron the in-phase and quadrature phase sub-channels is based on at leastone of a signal power level, a noise level, and an interference level oneach sub-channel.
 9. The WTRU of claim 6 wherein a target power value isset for the in-phase and quadrature phase sub-channels, respectively, tosupport a power balance between the in-phase and quadrature phasesub-channels.
 10. The WTRU of claim 6 wherein the physical resource is atime division multiple access (TDMA) resource.
 11. A method for use in asecond wireless transmit/receive unit (WTRU), for detectingtransmissions for one of a plurality of users on a same physicalresource, the method comprising: receiving, by the second WTRU, on aphysical resource in a same time slot, a first data for a first WTRU viaa first one of in-phase and quadrature phase sub-channels on thephysical resource and a second data for the second WTRU via a second oneof in-phase and quadrature phase sub-channels on the same physicalresource, wherein a transmit power of the in-phase sub-channel and atransmit power of the quadrature phase sub-channel are independent ofeach other; processing, by the second WTRU, the second data; and notprocessing, by the second WTRU, the first data.
 12. The method of claim11 wherein a ratio of the transmit power between the in-phase andquadrature phase sub-channels is within a predetermined range.
 13. Themethod of claim 11, wherein the transmit power on the in-phase andquadrature phase sub-channels is based on at least one of a signal powerlevel, a noise level, and an interference level on each sub-channel. 14.The method of claim 11 wherein a target power value is set for thein-phase and quadrature phase sub-channels, respectively, to support apower balance between the in-phase and quadrature phase sub-channels.15. The method of claim 11 wherein the physical resource is a timedivision multiple access (TDMA) resource.